For dynamic filtration in the area of ultra- and microfiltration, various separating devices are known, which are used in the form of filter cassettes, spiral coil modules and capillary or tubular modules.
In the German Auslegeschrift 2,920,253, a filter cassette is described, in which the fluid streams are distributed by boreholes disposed in the edge at least two opposite sides. The complicated flow guidance system and the small cross sections of the flow channels generally lead to an appreciable resistance to the flow in the filter cassettes. Such resistance is very undesirable.
Spiral coil filters are preferred for separating tasks, in which there are only small filter throughputs of about 100 L/m.sup.2 /hour as, for example, in the case of reverse osmosis and ultrafiltration. The long path, which the filtrate must cover in the filter pockets, also causes a high flow resistance here.
Capillary modules, like those used preferably for dialysis, reverse osmosis and ultra- and microfiltration, have a low flow resistance. They are also used successfully for separating tasks in the industrial sector. The possibilities of using this form of the module with its advantageous flow are restricted, however, by the limited availability of membranes in capillary or tubular form. The availability of planar membranes with different pore diameters and from different membrane materials is significantly greater than that of capillary membranes.